Greg Kahanamoku-Meyer
maiden name: Greg Meyer
Research directions
Arithmetic and number theory
Recently, I have been excited about creating new quantum circuits for arithmetic, factoring, and related tasks, with an emphasis on reducing qubit counts. Some of my results in this area include an entirely in-place (zero ancillas) algorithm for fast multiplication on quantum computers and a new quantum factoring algorithm that uses sublinear space (and depth)—that is, asymptotically fewer qubits than the number of bits in the value being factored. Soon I am also releasing a new logarithmic-depth QFT construction with extremely low ancilla count, which can be used with my fast multiplier to implement Shor's algorithm in near-linear depth using roughly 2n total qubits (see my poster on Thursday at QIP 2025!).
Classically-verifiable quantum computational advantage
Recent experiments have performed quantum computations that seem to be infeasible to reproduce with even the world's most powerful supercomputers.
However, a subtlety of those experiments is that the output of the computations is also computationally hard to verify—for the largest computations, it is not possible to directly show that the results are actually correct.
Much of my PhD work focused on tests of quantum computational advantage that are efficiently verifiable by classical computers, while still remaining hard to spoof.
Some of my results include:
- I broke a cryptographic proof of quantumness protocol that had stood for over a decade, by discovering a classical algorithm to extract its secret key.
- I then published a new proof of quantumness protocol for which spoofing the results is provably as hard as integer factorization, but which is more feasible than Shor's algorithm to implement in the near-term.
- I worked with experimentalists to perform a first small-scale demonstration of that protocol, using mid-circuit measurements to implement a quantum interactive proof in practice.
- I also worked with theory colleagues to improve the protocol further and extend its applicability, showing that it can also be used to constrain the behavior of an untrusted quantum device via cryptographically "certified qubits."
Massively parallel numerical quantum dynamics
Numerical study has proven to be one of the core tools for exploring the emergent properties of many-body quantum systems. I am the main author of the dynamite library, which provides extremely fast time evolution and eigensolving for numerical quantum many-body spin chain physics, parallelized using MPI and GPU acceleration. The backend is written in C and CUDA C++; the library exposes a Python frontend with an intuitive interface for building and analyzing spin chain Hamiltonians. The library is already being used by a number of labs; a list of publications using it can be found on the project's homepage. I have published works that use dynamite to explore Floquet prethermalization, time crystals in such a prethermal phase, and many-body chaos in the Sachdev-Ye-Kitaev model. (The manuscript officially releasing dynamite is in preparation). I also have published works using the LOBPCG algorithm to drastically reduce memory usage for mid-spectrum eigensolving of large many-body quantum Hamiltonians, in particular to explore the phenomenon of many-body localization.
Outreach & equity
As a postdoc, I currently volunteer as part of the following program:
QuERY: Quantum Engineering Research and You
Joint Harvard-MIT program mentoring high school students in Bellaire, TX about various subfields of quantum science, as well as generally about finding your path in science and life.
During graduate school, I was involved with the following organizations:
IGenSpectrum
Student group for the LGBTQ+ community in Berkeley Physics. I served as an officer.
Respect is Part of Research
Annual workshop aimed at improving department climate and preventing sexual violence and sexual harassment. I served each year as a facilitator, and helping to organize the workshop.
Bay Area Scientists in Schools
Teaching science lessons to elementary school students around the Bay Area. I participated as a teacher, and a member of the Steering Committee.
Please contact me or follow the links above if you're interested in getting involved with any of these organizations!
Talks and presentations
If you would like me to speak, feel free to contact me!
2025-02-27, QIP 2025.
"Factoring in near-linear depth using 2n+O(n/log n) qubits." (poster)
2024-11-19, IBM Quantum.
Guest seminar.
"The Jacobi factoring circuit: classically-hard factoring in sublinear quantum space and depth." (1 hr) [slides]
2024-10-03, MIT Quantum Information Science group.
Quantum Information Processing Seminar.
"Factoring in near-linear depth with roughly 2n qubits." (1 hr)
2024-09-27, Harvard University.
Yao group meeting.
"The pursuit of a free lunch: factoring in low depth with few qubits." (2 hr)
2024-09-11, University of Maryland.
QuICS seminar.
"Achieving low circuit depth with few qubits, for arithmetic and the QFT." (1 hr)
2024-05-16, Google Quantum AI.
Qualtran group meeting.
"Fast integer multiplication without ancillas." (1 hr) [slides]
2023-11-02, University of Hawaiʻi at Mānoa, Department of Physics and Astronomy.
Department colloquium.
"How to prove you have built a quantum computer." (1 hr) [slides]
2023-10-26, Google Quantum AI.
Seminar.
"Fast integer multiplication with very few ancillas." (1 hr) [slides]
2023-10-25, Caltech Institute for Quantum Information and Matter.
IQIM seminar.
"Fast integer multiplication with very few ancillas." (1 hr.) [slides]
2023-10-20, MIT Quantum Information Science group.
Quantum Information Processing Seminar.
"Fast quantum integer multiplication with very few ancillas." (1 hr) [slides]
2023-10-19, Harvard University.
Quantum information seminar.
"Fast quantum integer multiplication with very few ancillas." (1 hr) [slides]
2023-07-14, Simons Institute Summer Cluster Workshop.
Lightning talk.
"Fast integer multiplication with almost no ancillas." (20 min) [slides] [video]
2023-03-01, IBM Quantum.
Guest seminar.
"Cryptographic protocols for classically-verifiable quantum advantage and more." (1 hr) [slides]
2022-08-04, CLEAR Project.
PubScience.
"Quantum computing: how to do math with atoms, and how to trust the answers" (1 hr) [slides]
2022-05-03, UC Berkeley.
Guest lecture, CHEM 195/295: Special topics in Quantum Computing.
"Classical verification of quantum computation." (1.5 hr) [slides]
2022-03-15, APS March Meeting.
Quantum Digital and Analog Algorithms [Focus] (invited).
"Classical verification of quantum computational advantage." (30 min) [slides]
2022-02-22, Harvard University.
CMT Kid's Seminar.
"Classical verification of quantum computational advantage." (1 hr) [slides]
2022-02-09, Quantum Systems Accelerator (QSA).
Science session.
"Classical verification of quantum computational advantage." (15 min) [slides]
2021-11-10, IBM Quantum.
Quantum computing seminar.
"Classical verification of quantum computational advantage." (1 hr) [slides]
2021-10-08, MIT cryptography and information security.
CIS seminar.
"Classical verification of quantum computational advantage." (1.5 hr) [slides]
2021-09-29, NSF Challenge Institute for Quantum Computation (CIQC).
Colloquium introduction.
"Computability and complexity (introducing Jarrod McClean)." (20 min) [video]
2021-09-28, Physics of Information and Quantum Technologies, IT Lisbon.
Group meeting.
"Classical verification of quantum computational advantage." (45 min)
2021-07-14, Simons Institute for the Theory of Computing.
Quantum Wave in Computing Reunion.
"Classical verification of quantum computational advantage." (45 min) [video]
2021-05-21, MIT Quantum Information Science group.
Quantum Information Processing Seminar.
"Classical verification of quantum computational advantage." (45 min)
2021-04-26, UT Austin quantum information center.
Group meeting.
"Classical verification of quantum computational advantage." (45 min)
2021-04-23, AIDE-QC.
All hands meeting.
"Classical verification of quantum computational advantage." (20 min)
2021-04-21, Quantum Systems Accelerator (QSA).
Science session.
"Classical verification of quantum computational advantage." (15 min)
2021-02-01, Quantum Information Processing (QIP 2021).
"An efficiently-verifiable test of quantum advantage." (poster)
2020-08-26, AIDE-QC.
Verification and debugging thrust meeting.
"Efficiently-verifiable quantum advantage."
2020-06-02, APS DAMOP 2020.
"An efficiently-verifiable test of quantum advantage." (poster)
2019-05-30, APS DAMOP 2019.
"A numerical study of many-body localization using LOBPCG." (poster)
2018-03-08, APS March Meeting 2018.
"A long range, pre-thermal time crystal in one dimension." (15 min)
2017-06-07, APS DAMOP 2017.
"Simulation of quantum many-body dynamics for generic strongly-interacting systems." (poster)
Papers
See my page at Google Scholar
GDKM = Gregory D. Kahanamoku-Meyer
† = authors in alphabetical order
PhD dissertation
GDKM. Exploring the Limits of Classical Simulation: From Computational Many-Body Dynamics to Quantum Advantage. Ph.D. dissertation, University of California at Berkeley, 2023 [link]
Articles
† GDKM, S. Ragavan, V. Vaikuntanathan, K. Van Kirk. The Jacobi Factoring Circuit: Quantum Factoring with Near-Linear Gates and Sublinear Space and Depth. (To appear at STOC 2025). [arxiv] [eprint]
GDKM, N. Yao. Fast quantum integer multiplication with zero ancillas. arXiv:2403.18006 [arxiv]
GDKM. Forging quantum data: classically defeating an IQP-based quantum test. Quantum 7, 1107 (2023) [arxiv + journal]
† Z. Brakerski, A. Gheorghiu, GDKM, E. Porat, T. Vidick. Simple Tests of Quantumness Also Certify Qubits. CRYPTO 2023 [arxiv] [conf. proceedings]
GDKM*, D. Zhu*, L. Lewis, C. Noel, O. Katz, B. Harraz, Q. Wang, A. Risinger, L. Feng, D. Biswas, L. Egan, A. Gheorghiu, Y. Nam, T. Vidick, U. Vazirani, N. Yao, M. Cetina, C. Monroe. Interactive cryptographic proofs of quantumness using mid-circuit measurements. Nat. Phys. 19, 1725–1731 (2023) [arxiv] [journal]
* Co-first-authored paper
GDKM, S. Choi, U. Vazirani, N. Yao. Classically-verifiable quantum advantage from a computational Bell test. Nat. Phys. 18, 918–924 (2022) [arxiv] [journal]
R. Van Beeumen, K. Ibrahim, GDKM, N. Yao, C. Yang. Enhancing scalability of a matrix-free eigensolver for studying many-body localization. The International Journal of High Performance Computing Applications, 36(3), 307–319 (2022) [arxiv] [journal]
B. Kobrin, Z. Yang, GDKM, C. Olund, J. Moore, D. Stanford, N. Yao. Many-Body Chaos in the Sachdev-Ye-Kitaev Model. Phys. Rev. Lett. 126, 030602 (2021) [arxiv] [journal]
F. Machado, D. Else, GDKM, C. Nayak, N. Yao. Long-Range Prethermal Phases of Nonequilibrium Matter. Phys. Rev. X 10, 011043 (2020) [arxiv] [journal]
R. Van Beeumen, GDKM, N. Yao, C. Yang. A scalable matrix-free iterative eigensolver for studying many-body localization. HPCAsia2020: Proceedings of the International Conference on High Performance Computing in Asia-Pacific Region (2020) [conf. proceedings]
F. Machado, GDKM, D. Else, C. Nayak, N. Yao. Exponentially Slow Heating in Short and Long-range Interacting Floquet Systems. Phys. Rev. Research 1, 033202 (2019) [arxiv] [journal]
Peer review
Publications and conferences for which I have reviewed papers include Physical Review X, Physical Review X Quantum, npj Quantum Information, QIP 2022, QCE 2023, QIP 2023, QIP 2024, TQC 2024, ITCS 2025, QIP 2025, and QCTIP 2025.
About me
I grew up in Vermont, and enjoy archery, bouldering, Ultimate, and generally being outdoors.
My family is German and Czech, the name "Kahanamoku" comes from my spouse, who is Hawaiian.
I speak English natively, and have varying levels of conversational proficiency in French, Spanish, and Hawaiian.
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